This invention relates broadly to a demand defrost time clock control circuit for refrigeration systems. More particularly, this invention relates to a method and apparatus for controlling the defrost cycle in a refrigeration system to initiate defrost on demand rather than by time. More particularly, this invention relates to a method and apparatus for initiating defrost on demand by terminating operation of a conventional clock timer motor prior to initiation of an otherwise timebound defrost whereupon the defrosting unit operates by and in response to a demand of the system for defrosting.
Systems are known to the art for controlling the defrost of one or a plurality of refrigeration units. Such systems operate generally at either regular timed intervals or upon a demand based upon the sensing of a frost accumulation on the refrigeration coils of the unit or in response to other frost accumulation parameters. A typical time demand type of system includes a conventional, commercially available defrost clock having a timer motor to initiate defrost on a periodic basis. For example, in a typical sequence, the clock timer motor operates to initiate two defrosts per day by alternatively controlling a compressor in the refrigeration unit and the defrost heaters for the unit. Such systems have proven quite reliable and have achieved significant field acceptance. Moreover, such systems have significant failsafe features.
However, since time bound defrost cycles utilize a significant amount of energy, it is desirable to reduce the energy requirements for defrosting by eliminating unnecessary defrost cycles, or at least reducing their number. Thus, it is an overall aim of this invention to produce a demand defrost control system for refrigeration systems rather than a time bound defrost control system while at the same time continuing to provide the proven reliability, field acceptance, and failsafe features of conventional defrost time clocks. In conjunction with this aim, it is desirable to be able to set a minimum time between defrosts on the clock and to utilize, where desirable, optional multiple sensors at differing sensing points in such a manner that any one of such sensors could initiate a defrost cycle in the refrigeration system.
The reduction in the number of defrosts yields an improved product life and quality as well as the reduction in the energy needed. Energy savings occur because it requires energy to heat the previously refrigerated but frosted area to a temperature high enough to melt the frost, and the heat provided to the refrigerated area during the defrost cycle must be removed at the end of the defrosting period. By way of example, the process of removing the defrost heat in a refrigeration unit typically takes about the same amount of energy as it takes to melt the frost at frozen food and ice cream temperatures.
Thus, it is an overall object of this invention to provide a demand defrost initiated cycle utilizing a conventional defrost clock and conventional defrost sensors.
These and other objects and aims of the invention will become apparent from the review of the following written description taken in conjunction with the accompanying drawings.